Video Transcript
Nutrients required by plants can be
divided into two groups: macronutrients and micronutrients. Which of the following best
explains the difference between the two? (A) Macronutrients are large
molecules compared to micronutrients, which are much smaller-sized molecules. (B) Macronutrients are required in
large amounts by the plant, whereas micronutrients are required in very small
quantities. (C) Macronutrients take longer to
break down in a plant than micronutrients. Or (D) micronutrients are rarely
found in soil and more difficult for plants to obtain than macronutrients.
This question deals with nutrient
requirements in plants. To make space for a brief review of
this topic, we’ve temporarily cleared our answer options. We’ll bring them back once we’re
ready to select the correct one.
Unlike humans and other complex
animals, plants do not have digestive systems to break down their food and provide
their cells with nutrients. Instead, plants obtain some of
their nutrition from sugars made during photosynthesis. The remainder comes from essential
minerals. A mineral is an inorganic substance
that cannot be synthesized by an organism but instead must be ingested or
absorbed. Plants absorb minerals from the
soil through their roots, often in the form of ions, which are electrically charged
atoms or molecules.
The question reminds us that the
essential minerals required by plants are divided into two main groups,
macronutrients and micronutrients. You may already know that the
prefix macro- means large or long, which helps us remember that macronutrients are
minerals that are needed in relatively large amounts. A lack of any of these elements
will result in poor growth, compromised reproduction, and eventual death of the
plant.
For example, nitrogen is necessary
to form amino acids. Amino acids form bonds to create
peptides, such as the dipeptide shown in the diagram. Peptides, in turn, bond to form
proteins. Proteins are one of the four major
biological macromolecules in living organisms. So plants require large amounts of
nitrogen. If a plant is grown in soil with
insufficient nitrogen, its leaves will turn yellow. It may also stop growing. And if the nitrogen deficiency
continues for long enough, the plant will eventually die.
The prefix micro- means small,
which reminds us that micronutrients are minerals that are needed in relatively
small amounts. Most micronutrients, which are
sometimes referred to as trace elements, act as cofactors in enzymatic
reactions. A cofactor is a nonprotein
component of an enzyme that helps the enzyme catalyze a specific reaction. For example, iron is a cofactor for
enzymes that are involved in cellular respiration and photosynthesis. This means that although the amount
of iron needed by plants may be small, it is critical for survival and optimal
growth, as are all the essential micronutrients.
Now, let’s bring back our answer
options and take another look at our question. It asks us for the best explanation
of the difference between macro- and micronutrients. The word “best” tells us that
although more than one of the answer options may be true, we need to choose the one
that most accurately summarizes the major difference. Based on what we have reviewed,
option (B) is correct. The best explanation of the
difference between macro- and micronutrients is that macronutrients are required in
large amounts by the plant, whereas micronutrients are required in very small
quantities.
